These types of reflector antennas are chiefly used because they are straightforward and inexpensive to manufacture. They also provide greater antenna efficiency and lower side lobes in the radiaton pattern than is the case when the feed element has to be supported by diagonal struts. The drawback with the latter configuration is that the main reflector becomes blocked. A self-supported feed is also easely accessible from the back of the reflector, thus is frequently selected when it is best to locate the transmitter and/or the receiver there. This also reduces the loss that occurs when the waves have to be led in a cable along one at the support struts.
A. Chlavin, "A New Antenna Feed Having Equal E and H-Plane Patterns", IRE Trans. Antennas Propagat., Vol. AP-2, pp. 113-119, Jul. 1954, describes a reflector antenna with a self-supporting feed. However since this antenna uses a waveguide with a rectanguler cross-section, it can only transmit or receive waves with one particular linear polarization.
C. C-Cutler, "Parabolic-antenna design for microwaves", Proc. IRE, Vol. 35, pp. 1284-1294, Nov. 1947, describes a dual polarized reflector antenna with two variants of a self-supporting feed, called the "ring focus" and the "waveguide cup" feeds respectively. A circular waveguide is used in these two feeds with a reflecting object in front of the waveguide opening, this reflector being respectively shaped like a flat disc and a cup. Both of these feeds unfortunately produce high cross-polarization within the main lobe the radiation pattern.